Extending Odoo Models Safely: Maintaining Compatibility During Upgrades

# WRONG - Do NOT do this
/opt/odoo/addons/sale/models/sale.py  # Modifying core file!

# In sale.py, you add a custom field:
class SaleOrder(models.Model):
    _name = 'sale.order'
    custom_field = fields.Char()  # You added this directly to core file

# RIGHT - Create a custom module
/opt/odoo/addons/custom_sales/models/sale_extension.py

class SaleOrder(models.Model):
    _inherit = 'sale.order'  # Extend, don't modify
    custom_field = fields.Char()  # Added via inheritance

class SaleOrder(models.Model):
    _inherit = 'sale.order'
    
    x_custom_note = fields.Char()  # x_ prefix = custom field
    x_is_priority = fields.Boolean()  # Always prefixed
    x_estimated_arrival = fields.Date()

class SaleOrder(models.Model):
    _inherit = 'sale.order'
    
    custom_note = fields.Char()  # No x_ prefix, could conflict
    is_priority = fields.Boolean()  # Dangerous, Odoo might add this

# WRONG - Missing super()
class SaleOrder(models.Model):
    _inherit = 'sale.order'
    
    def action_confirm(self):
        """Confirm the order."""
        print("Order confirmed")
        return True

# RIGHT - Calls super()
class SaleOrder(models.Model):
    _inherit = 'sale.order'
    
    def action_confirm(self):
        """Confirm the order and do custom logic."""
        # Call parent method first
        result = super().action_confirm()
        
        # Then do custom logic
        print("Order confirmed")
        self.x_custom_flag = True
        
        return result

# WRONG - Redefining field
class SaleOrder(models.Model):
    _inherit = 'sale.order'
    
    # Trying to make order_date required (it already exists)
    order_date = fields.Datetime(required=True)  # Redefining!

# SAFEST - Use a computed field or validation
class SaleOrder(models.Model):
    _inherit = 'sale.order'
    
    @api.constrains('order_date')
    def _check_order_date(self):
        """Validate that order_date is set."""
        for record in self:
            if not record.order_date:
                raise ValidationError("Order date is required")

<!-- WRONG - Fragile xpath -->
<xpath expr="//div[1]/group[1]/field[3]" position="after">
    <field name="x_custom_field"/>
</xpath>

<!-- RIGHT - Stable xpath using unique attributes -->
<xpath expr="//field[@name='order_date']" position="after">
    <field name="x_custom_field"/>
</xpath>

custom_module/
├── models/
├── views/
├── migrations/
│   ├── 18.0.1.0.0/
│   │   └── pre-migration.py
│   ├── 19.0.1.0.0/
│   │   ├── pre-migration.py
│   │   ├── post-migration.py
│   │   └── my-migration.py

def migrate(cr, version):
    """
    Migration script for moving from version 18 to 19.
    Runs BEFORE module code is updated.
    """
    # Backup old field data before changing type
    cr.execute("""
        ALTER TABLE sale_order
        ADD COLUMN x_priority_old VARCHAR;
    """)
    cr.execute("""
        UPDATE sale_order
        SET x_priority_old = x_priority_number;
    """)

def migrate(cr, version):
    """
    Runs AFTER module code is updated.
    Transform data from old format to new.
    """
    # Convert old field to new format
    cr.execute("""
        UPDATE sale_order
        SET x_priority = CASE 
            WHEN x_priority_old = '1' THEN 'low'
            WHEN x_priority_old = '2' THEN 'medium'
            WHEN x_priority_old = '3' THEN 'high'
            ELSE 'low'
        END;
    """)
    
    # Drop old field
    cr.execute("""
        ALTER TABLE sale_order
        DROP COLUMN x_priority_old;
    """)

# Wrong - Same version for 17, 18, 19
{
    'name': 'Custom Sales',
    'version': '1.0.0',  # Not version-specific!
}

# Right - Version-specific
{
    'name': 'Custom Sales',
    'version': '19.0.1.0.0',  # 19 = Odoo 19, 1.0.0 = your version
    'depends': ['sale'],
}